Air assist nozzle



SPRAY coNE MEAN DROP SIZE ocr. 2s, 1969 HESIMMNS ETAE 3,474,970

AIR ASSIST NOZZLE Filed March i5, 1967 r E 8o A|R ASSnST i zs SPRAY"QZZLE PRESSURE oPERATEo .x 7o, SPRAY NozzLE SOL PRESSURE oPERATEo s200k SPRAY NOZZLE V00@ 8 Ill z :u o co r m g u 5 E '0' A|R ASSIST '5SPRAY nozzLE 2o J f E m D FUEL PRESSURE w (Bom GASES) d D 0g 25 5o loozNvENToRs FUEL FLOW RATE (PPH) EUGENE R. H066 ROY C. KUHN HAROLD c.SIMMONS l E ATTORNEYSvv United States Patent O U.S. Cl. 239-404 5 ClaimsABSTRACT 0F THE DISCLOSURE Nozzle for spraying liquids especially fuelfor use in aircraft gas turbines and the like. Nozzle is of air assisttype characterized by merging of concentric conical air stream andconical fuel sheet at exit oriiice of nozzle.

The present invention relates as indicated to a nozzle and particularlyto a fuel nozzle of the air assist type for gas turbine and likeapplication.

'Ihe nozzle herein is in the class of liquid spraying devices in whichsome or all of the energy required to atomize and to disperse the sprayis supplied by a second fluid, such as air. Such devices take many formswith a variety of arrangements of liquid and gas passages and the gaspressures which are employed may be as high 4as several hundred poundsper square inch. In contrast, the present nozzle may be termed a lowpressure atomizer because the air pressure required for efiicientatomization ranges only from about 1/2 to 10 p.s.i. which pressure isespecially suited for use in aircraft gas turbines in view of thediiiiculty and expense of providing a source of high pressure airespecially under high altitude conditions.

One disadvantage of known air operated spraying devices is that thespray is concentrated in a stream of relatively small included coneangle, i.e., less than 60, whereas, in combustion applicationsgenerally, as well as in other fields of -application such as spraydrying, it is necessary to produce sprays having included cone angles ofthe order of 90 or greater.

A known advantage of air atomizing or spraying devices is the capabilityof atomizing liquids of relatively higher viscosities than canconveniently be atomized by using conventional liquid pressure operateddevices. In addition, because it is unnecessary to use high liquidsupply pressures, the liquid passage dimensions can be made larger thanotherwise required for a given flow rate, and thus the problems ofclogging of passages with contaminants is minimized.

Accordingly, it is a principal object of this invention to provide anair assist nozzle which, when employed for spraying fuel for combustionengines, achieves good atomization of fuels having a wide range ofviscosities', including fuels which are quite viscous at lowtemperatures as would be involved in high altitude flights.

It is another object of this invention to provide an air assist nozzlewhich improves the quality of atomization, i.e., the iineness of thespray, at very low fuel flow rates.

It is another object of this invention to provide an air assist nozzlewhich produces a hollow conical spray pattern of large included angle,and further, with capability of ready adjustment of the spray angle.

It is another object of this invention to provide an air assist nozzlewhich is economical to operate in terms of both low air pressure and lowair ow rate while yet achieving good atomzation.

It is another object of this invention to provide an air assist nozzlewhich enables the use of relatively large "ice size -fuel passages inorder to minimize problems resulting from fuel contamination.

It is another object of this invention to provide an air assist nozzlewhich has a very wide useful fuel flow range of, for example, :1 ascolnpared with the usual 4:1 range obtainable with liquid pressureoperated nozzles.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail a certain illustrativeembodiment of the invention, this being indicative, however, of but oneof the various ways in which the principle of the invention may beemployed.

In said annexed drawing: v

FIG. l is an elevation view of a fuel nozzle embodying the presentinvention as mounted on an air-fuel manifold;

FIG. 2 is a fragmentary cross-section view on much enlarged scale takensubstantially along the line 2-2, FIG. 1; and

FIG. 3 are comparative graphs of performance characteristics of thepresent air assist nozzle and a fuel pressure operated nozzle (withoutair assist).

Referring now more particularly to the drawing, the nozzle 1 herein ismounted in a dual manifold 2 for supplying air and fuel into therespective passages 3 and 4 in the nozzle 1. The nozzle 1 herein showncomprises tubular body and nozzle members 5 and 6 defining therebetweenthe air passage 3. The nozzle member 6 has, in the fuel passage 4thereof, a swirl member 7 provided with slots 8 which are disposed at anangle to the axis of the vortex chamber 9 so as to produce a swirlingfuel ilow having the general characteristics of a free vortex. The fuelis discharged through the orifice 10 which is coaxial with the vortexchamber 9, the discharge orifice 10 being extended as shown in thedirection of fuel Vdischarge in a substantially conical lip 11terminating in a sharp edge 12.

Surrounding the vortex chamber 9 is the annular air passage 3 the innerand outer walls of which converge conically through swirl producingvanes or slots 14 in nozzle member 6 to a minimum diameter and thenflares conically outward. The air flow is further guided by the lip 15which is concentric with the vortex chamber discharge orifice 10 andterminates in the sharp edge 16.

The cross-section area for air flow is designed to be continually4decreasing until the point 17 is reached and this is made as close asis practical to the edge 12 of the fuel discharge orice 10. Accordingly,the highest air velocity is produced at the point 17, and the shape ofthe surface 15, in conjunction with the use of swirl slots 14 producesan air ow discharge characterized as tending to follow the surface of acone. It should be noted that the included angles of the lips 11 and 15are sub'- Stantially the same.

In operation, when fuel enters the vortex chamber A9, a vortex is formedhaving an air core as shown and the fuel discharges from the orifice 10as a hollow conical sheet which is constrained to flow along the lip 11and leave ythe edge 12 as a very thin conical sheet. At this point thethin conical sheet of fuel is immediately acted upon by the highvelocity air stream and broken into a supplyfof small dropsl whichcontinue under the combined momentum of the fuel and air streams tofollow a substantially conical path until acted upon by other forcessuch as air turbulence. By these means, advantage is taken of thenatural property of the vortex chamber 9 of tending to produce a conicalsheet of fuel andthe air is employed to constitute the break-upmechanism in producing a spray from the sheet.

A further important feature of the present invention is that when a highviscosity fuel is used at relatively low fuel pressure, the fuel issuingfrom the discharge orifice 10 has insufficient momentum to follow aconical path, but herein the high velocity air as it passes the point17, acts in effect as a venturi in which, by reason of the lowering ofstatic pressure due to high air velocity, the fuel is sucked outwardfollowing lips 11 and 15, and is atomized by the air stream. Thischaracteristic is demonstrated in FIG. 3 which shows that the supplycone angle can be maintained by the air assist nozzle 1 down to very lowfuel flow rates. In fact, this flow rate is far below the point at whicha conventional fuel pressure operated nozzle ceases to produce arecognizably conical discharge.

In the design of the fuel vortex chamber 9 the inlet passage 4 anddischarge orifice 10 dimensions can be chosen without regard to theatomizing process. In other words, the dimensions can be maximized andlow fuel spray pressures employed. The geometry and sizes of the airflow passage 3 do not appear to be critical until the point 17 isreached and it has been found that the width ofthe air annulus at point17 should rbe of the same order of magnitude as the dimensions of thefuel inlet slots 8 thus indicating no greater precision to be requiredin the manufacture of the air passages 3, and 14 than in the parts ofthe fuel vortex chamber 9. The effectiveness of this nozzle 1 inproducing finely atomized sprays is due to the high kinetic energy ofthe air stream. Por example, for equal flow rates of air and fuel and anequal pressure drop for lboth fluids the kinetic energy of the air canbe shown to be about 600 times greater than the fuel. In a specificexample, therefore, where it is required to atomize a fuel flow rate of1 p.p.h., the fuel pressure being no greater than l p.s.i., if 1 p.p.hof air at a pressure drop of 1 p.s.i is supplied, the atomizing power ofthe nozzle 1 is similar to that which would be produced by a pressureoperated fuel nozzle operating at about 300 p.s.i. fuel pressure. Inpractice, the pressure operated nozzle would have eX- tremely smalldimensions and would be very limited in the flow range available withoutusing very high fuel pressures.

In the present nozzle 1 the cone angle of the spray can readily bechanged .by simply changing the angles of the lips 11 and 15 withoutchanging the proportions of the fuel vortex chamber 9 or the internalair passages 3 and 14.

Referring to FIG. 3, it can be seen that with the present nozzle 1 thespray cone angle (curve 18) remains substantially constant, i.e., 90 atall fuel liow rates Ibetween 0 and 100 p.p.h., whereas, a fuel pressureoperated nozzle for a 90 spray cone angle (curve 19) does not attainthat spray cone angle until the flow is about 60 p.p.h., the vanglegradually increasing to 90 from about 60 at 25 p.p.h.

In FIG. 3 the curve 20 represents the fuel supply pressure vs. fuel flowrate characteristics of both the nozzle 1 of the present invention and aconventional fuel pressure operated nozzle. With reference to fuel flowrange, the conventional fuel pressure operated nozzle (curve 21) has auseful flow range of about 4:1 with an average droplet size of about 120microns at 100 p.p.h. with the droplet size increasing to about 220microns at 25 p.p.h., that being the limit of a usable fuel spray.Contrary to that, the present nozzle 1 (curve 23) has a usable flowrange of about 100:1, since from a rate of fuel -ffow of just greaterthan 0 p.p.h. the droplet size ranges from less than 50 microns at suchlow flow to a maximum of about 140 microns at about 40 p.p.h. flow andthen gradually down to about 120 microns tat 100 p.p.h.

With the present nozzle 1 even with a high viscosity fuel at lowtemperature there is no problem in relighting the engine even at 25,000altitude. At high rates of fuel flow it has been found that the air flowcan be discontinued if desired, although the results are better withswirling low pressure air. In some cases satisfactory results may beobtained by omitting the air swirl slots 14.

`In any case, it has :been found that only a low air pressure of from1/2 to 10 p.s.i. is required and in the curves of FIG. 3, the airpressure was but 1 p.s.i. and the fuel has a viscosity of 12centistokes.

We therefore particularly point out and distinctly claim as ourinvention:

1. A spray nozzle comprising a nozzle !body assembly definingtherewithin a liquid passage having a vortex chamber to impart awhirling motion to the liquid flowing through -said passage and havingan outwardly flared conical discharge orifice through which the liquidis discharged in the form of a hollow cone, and an annular air passagedisposed concentrically around said orifice for flow of air to mergewith the liquid cone as the latter flows past the end of said dischargeorifice thus to break up the liquid into Ia fine conical spray, the wallof said discharge orifice and the inner wall of said air passageconverging toward each other, said air passage being of minimum radialcross-section width substantially at the end of said orifice, and theouter wall of said air passage extending radially and axially beyond theend of said discharge orifice thus to form a conical surface havin-g anincluded angle substantially the same as the included angle of theorifice along which the air stre-am flows to assist in break up of theliquid as it leaves the confines of said orifice.

2. The spray nozzle of claim 1 wherein said air passage has convergingconical inner and outer walls effective to impart high velocity fiow ofair as it merges with the liquid.

3. The spray nozzle of claim 2 wherein said air passage has spin slotstherein to impart whirling motion to the air 'as it merges with theliquid.

4. The spray nozzle of claim 2 wherein said inner and outer conicalwalls immediately upstream of the end of said orifice are flaredoutwardly to turn the increasing velocity air flow therethrough so as toflow in the form of a conical stream along the liquid as the latterleaves the confines of said orifice.

5. The spray nozzle of claim 4 wherein the outwardly flared inner wallof said air passage merges with said orifice to locate said air passageclosely adjacent the edge of said orifice.

References Cited UNITED STATES PATENTS 2,643,916 6/ 1953 White et al239-405 3,013,732 12/1961 Webster et al 239-406 3,346,412 10/ 1967Siegenthaler et al 239-405 2,566,788 9/ 1951 Berggren et al 239-4042,595,759 5/1952 Buckland et al 239-404 2,703,260 I3/ 1955 Olson et al239-404 EVERETT W. KIRBY, Primary Examiner U.S. Cl. X.R 239-406

